The work described here was aimed towards high efficiency light emitting diodes (LEDs), thereby compromising on directionality and narrow spectrum. At present our efforts have yielded devices which have an external quantum efficiency (QE) of over 22%. This is believed to be a record QE for planar LEDs. This result relies on both careful design and material growth. For the design we developed a simulation tool which proves useful in selecting interesting structures and interpreting experimental results. The theoretical analysis includes the guided modes, reabsorption of light by the active material and subsequent photon recycling. The material is grown with MOVPE, which yields high quality material as well as allowing excellent control over layer thickness and composition. In the first part we highlight the main characteristics of the theoretical model and deal with some key issues in the design of high efficiency microcavity LEDs (MCLEDs). In part two the main experimental results are discussed. (6 pages)

High efficiency substrate emitting microcavity InGaAs/(Al)GaAs single QW LEDs are reported. The influence of the reflectivity of the bottom GaAs/AlAs DBR and cavity dimensions have been investigated. The best results obtained include peak external quantum efficiencies of 6.2%, and an intensity of 210 µW/steradian at 10 mA.